How safe is the MMR vaccine?

An investigation is underway into the deaths of two babies in Samoa earlier this month shortly after they received MMR vaccine. In her blog, Dr Helen Petousis-Harris, director of the Immunisation Advisory Centre, answers some of the questions raised by the tragedy.

July 23, 2018

On Friday 6 July 2018 in the tiny Pacific nation of Samoa, two babies died shortly after receiving the MMR vaccine. How could this happen? Lots of discussion has been centred around this tragedy, and even more questions. Here are some responses to questions I have been asked.

About MMR vaccines

MMR vaccines were originally developed in the 1970s to protect against measles, mumps, and rubella in one convenient jab. However, there is a long history of the development and use of measles-containing vaccines that extends back to the 1960s.

The measles-containing vaccines are called live vaccines. This is because the viruses in the formulation are viable; they can replicate. The viruses need to replicate to get the body to make an immune response that will be protective against disease, but they have also been weakened so they are unable to cause disease. These vaccines are extremely effective, with measles and rubella vaccines likely providing lifelong protection.

It is hard to estimate how many people in the world have received these vaccines, but in 2016 85 per cent of one-year-olds had received a dose of measles-containing vaccine, like the MMR. Given that each year the world welcomes over 130 million newcomers, the number of people having received these vaccines will be well in the billions.

The point is, an awful lot of vaccine has been used and many lives saved!

How safe are MMR vaccines?

Short answer: Very.

Longer answer: Relatively common events associated with MMR vaccine are: fever and/or mild rash 6–12 days after immunisation due to the measles component; fever and/or mild swelling under the jaw 10—14 days after immunisation due to the mumps component; and fever, mild rash and/or swollen glands 2—4 weeks after immunisation due to the rubella component. Temporary joint pain 2–4 weeks after immunisation is more common in adult women than children.

Rare adverse events associated with MMR vaccine: Temporary low platelet count about 1/30,000; convulsion associated with a fever about 1-2 per million dose; encephalitis less than one per million; infection-free meningitis about one per 800,000 to one per million; and anaphylaxis one per million.

Yes, there are some rare but serious risks.

How do we know? Nearly 60 years of safety surveillance and studies, the nature of which I have summarised in these pages previously.

Risks from those diseases

Here are some figures on the risks from measles, mumps, and rubella.

Measles: Ear infection (otitis media), diarrhoea, pneumonia, low platelet count, encephalitis (brain inflammation) for around one person out of 1000—2000 cases; weakened immune system; hospitalisation for around one to two people out of 10 cases; death for around one person in 1,000 cases, despite treatment; and degenerative brain disease for around one person out of 100,000 cases, occurs years later and is always fatal. Measles during pregnancy increases the risk of miscarriage or premature birth.

Mumps: Fever, headache, swelling and pain of one or more glands under the jaw; viral meningitis for up to 15 people out of 100 cases; temporary deafness for around four people out of 10 cases and permanent deafness for around one person out of 15,000 cases; inflammation of the testicles or ovaries in adolescents and adults; nerve, joint, kidney, heart inflammation; encephalitis (brain inflammation) for around one person out of 6,000 cases, which may result in death for one person out of 100; death for one to two people out of 100,000 cases; and mumps during early pregnancy increases the risk of miscarriage.

Rubella: Some cases have no symptoms, which increases the risk of exposing pregnant women to the disease. Rash and painful swollen glands; joint pain in adolescents and adults; low platelet count; and encephalitis (brain inflammation) for around one person out of 6,000 cases. Rubella during early pregnancy can cause severe abnormalities in unborn babies, including deafness, blindness, heart defects, and brain damage.

People who should forego the MMR vaccine

Because the MMR vaccine has live (albeit weak) viruses in it, it should not be given to anyone who:

has experienced a severe allergic reaction (anaphylaxis) to a previous dose of any measles, mumps or rubella containing vaccine or any of the vaccine components.

is acutely unwell. The presence of a minor infection is not a reason to delay immunisation.

has a diagnosed weakness of their immune system.

received another live injected vaccine, including varicella (chickenpox) or BCG vaccines, within the previous month.

is currently pregnant (women should delay pregnancy for one month after having the vaccine). However, there is no evidence of harm if this happens.

How can vaccination with MMR go wrong?

Apart from the known risks of the MMR vaccine above, other things can go wrong:

The MMR vaccine often comes as a lyophilised (freeze-dried) powder. It needs to be reconstituted with a diluent – in this case sterile water for injection. There have been tragic occasions where instead of the vaccine diluent provided with the product, another substance was inadvertently used to reconstitute the vaccine. If this substance is something like morphine, adrenaline, or anaesthetic the consequences are likely to be disastrous. An example of this occurred in Syria, where it appears likely the vaccine was mixed with a muscle relaxant from the same fridge. Fifteen children died and a number of others were very ill.

Contamination of the vaccine by bacteria can happen when multi dose vials are used. While in New Zealand we use single dose vials, some countries use vials that contain five or 10 doses. Once reconstituted, these need to be used within a few hours then discarded. If they are left lying around in a warm place, bacterial growth can set in. The MMR vaccine has no preservative to stop this from happening. Using a damaged product can result in overwhelming sepsis and/or poisoning from toxins that the bacteria produce. A terrible case in the Sudan involved untrained workers and a single syringe for the whole four-day campaign, and no access to cold chain. Like the Syrian disaster, fifteen children died and hundreds were ill.

However, even when the vaccine has been stored and handled properly, things can still go wrong if a person has:

an underlying deficiency of the immune system. Sometimes people with an immune deficiency, such as being on immune-suppressive drugs like steroids, chemotherapy, or having an inherited immune deficiency, or HIV infection, or undiagnosed blood cancer, may be inadvertently vaccinated with a live vaccine. What happens? Usually nothing. However, there is a risk that their immune system isn’t working well enough to control the replicating vaccine virus. This could develop a disseminated vaccine-related infection.

an undiagnosed underlying condition; something that has remained dormant, waiting for the right trigger. Many infectious diseases do this, such as influenza, herpes, hepatitis and chicken pox. Very occasionally, a vaccine can do this too.

Finally, despite best practice, some events are unavoidable. Very, very rarely a previously healthy person will have a serious allergic reaction to the MMR vaccine.

What happened in Samoa?

Until the investigations have been completed and the results reported, we cannot say what happened.

However, given that the batch of vaccine involved had been in use in that country since August last year, and given the same batch of vaccine has been used in South American countries and the Caribbean island nations without incident, it seems unlikely that there was anything wrong with the vaccine.

The reports from the parents of the children affected on Friday indicate the reactions occurred within minutes after vaccination. This would preclude a response to the vaccine viruses as this takes at least a week. While anaphylaxis occurs within minutes and can be fatal when not treated, the odds of seeing this twice in a day at the same place, given a chance of one in a million doses, is literally astronomical.

1 COMMENT

Sure it’s very safe…if you aren’t a grown woman. 26% risk of arthritis for women. I don’t think a 26% risk of such a terrible side effect makes it safe for women. I’d give it to a child, I’d tell a man to get it, but I wouldn’t get it, and would strongly advice that especially older women don’t.